There are many types of systems for collecting solar energy as well as for concentrating the rays linearly for heating a fluid to a high temperature, which is generally used to produce electricity.
A type of concentrator existing today is the one which uses linear Fresnel lenses for concentrating the rays of the sun on the fluid. The system is basically formed by the lens, a collector which receives the concentrated radiation and the supporting structure and mechanisms. A frequent problem in the existing systems is that if it only tracks the rays of the sun on an axis in an east-west trajectory as the day advances, or north-south for different seasons of the year, this involves a loss of efficiency of the system as it loses concentration in the collection line. This is due to the use of linear concentrating lenses, because the focal point of maximum concentration varies depending on the angle of incidence of the radiation, affecting the efficiency of the installation.
This technical problem has only been solved up until now by means of systems for movement on two axes perpendicular to one another which allow tracking the sun in all its positions, whereby the angle of incidence of the rays of the sun on the lens is always perpendicular with respect to both axes, maintaining the point of maximum concentration invariable, i.e., the focal distance between lens and collector is constant. To achieve high temperature jumps, collectors must be connected in series, and the manner of maximizing efficiency is by placing said collectors forming very long straight lines, and this is not allowed by the two-axes system described above.
Patent WO2007/087343 describes a system which allows movement in both the east-west axis and in the north-south axis to optimize the use of the energy for any angle of incidence. However, the system is based on spheres which rotate about two axes and concentrate the rays individually, which prevents optimizing the efficiency in linear concentrators.
GB 1590841 discloses a solar tracker with refractive based solar energy concentration comprising a movable structure to which one or more linear fluid concentration lenses and one or more mutually parallel linear collectors rigidly interconnected by a structure, are attached. Each of the linear collectors is arranged to capture solar rays concentrated by one of the concentrating linear lenses. This solar tracker also includes drive means operationally connected to pivot this movable structure with respect to a supporting structure about a first longitudinal axis parallel to these linear concentrating lenses and to enable said linear collectors to track a relative movement of the sun (seasonal movement). The lens also is rotatable relative said movable structure about a transversal axis thereof, perpendicular to said first longitudinal axis, to track the sun's hourly movement. A drawback of the proposed solution is that, in spite the lenses can rotate around said transversal axis, the distance between the linear concentrating lenses and the collectors is fixed, so it is not possible to vary it in order to optimize the conditions of solar radiation concentration on said collectors. Moreover the tilting of the lens can not provide an adequate concentration on the collector at different positions.
GB 1590841 provides the features of the preamble of claim 1
US 2008/0295825 discloses a lens system with correction of focal distance for concentration of solar radiation on a collector, providing some means to move a set of linear concentrating lenses towards or away a fixed collector, or to move a collector with regard to stationary concentrating lenses, through a circular oscillating movement (rotation around the center points of a circular disks or rotating bars) of the set of lenses or collector. Such an oscillating circular movement has the drawback that the concentration capacity of the lenses is not used at certain stages of the movement, thus producing shadows.